More and more couples are crossing borders in search of doctors who can provide fertility treatments banned in their own countries.

A BBC documentary has followed the progress of one couple,Alan and Louise Masterton, from Monifieth near Dundee, who attracted press attention because they want to select the sex of an IVF child.

Their only daughter, Nicole, was killed in an accident more than a year ago, and the couple already have four sons.

If we are playing God - is normal IVF playing God?

Louise Masterton

However, pre-implantation gender selection is not currently allowed by the UK's fertility treatment watchdogs.

Instead, they went to Italy where the procedure is approved.

Another woman, Jenny Jones, is in her late 50s, but still is hopeful that she can become pregnant following IVF using egg and sperm donors.

Doctors in this country are unanimous in turning away women of this age asking for IVF. They fear that the burden of risk on the mother is too high, as is the emotional scarring on the child of the potentially early death of its parent.

Jenny has been trying for almost a decade to find successful treatment abroad, followed by controversy at each step.

Sharia law

But this is not just one-way traffic. Couples from countries which have Sharia law may be disadvantaged if they have certain fertility treatments, particularly involving sperm donation.

Some travel, in secrecy, to London, or other European capitals, to receive treatment.

Jenny Jones hopes to become a mother at 57

The Mastertons believe that the birth of a new daughter will help heal the wounds left over from the death of their daughter.

Louise Masterton said: "We miss her so much. This has given us a focus to our grief, something to look forward to rather than look backwards.

"If we are playing God - is normal IVF playing God?"

She said that by choosing a girl, they were simply trying to restore the natural balance of the family.

'Perfectly good embryo'

However, the chairman of the UK's Human Fertilisation and Embryology Authority (HFEA), Ruth Deech, said that pre-implantation gender selection was not to be encouraged.

She said: "We tried to tell them that you shouldn't throw away perfectly good embryos because they are not girls."

She said there was a risk that the four sons might feel unwanted if the procedure went ahead.

I'm not quite sure why, when you reach the age of 50, your attitude to children is supposed to change. It doesn't

Jenny Jones

The Mastertons went to a clinic in Rome, where three eggs were extracted following hormone treatment.

However, only one was suitable for fertilisation, and the resulting embryo turned out to be male, and was not implanted.

The couple cannot afford any further cycles of fertility treatment, and are now campaigning for the HFEA to lift the restriction in the UK.

Ruth Deech: gender selection is undesireable

Jenny Jones' case first made newspaper headlines in the early 1990s, when it was revealed that a Rome clinic was preparing to try to make the 57-year-old pregnant.

Following the furore, her treatment was cancelled.

She said: "There is still a feeling that a woman who is older having a child is somewhat selfish, that they are doing it for their own malignant purposes.

"I'm not quite sure why, when you reach the age of 50, your attitude to children is supposed to change. It doesn't."

She is currently trying to recruit an egg donor who is prepared to help her. A clinic in Greece has said it will carry out the necessary procedure.

The UK has some of the most tightly regulated fertility treatment in the world, so it is unlikely that the number of couples desperate enough to go abroad will fall away in the next few years.

Modern Times: Fertility Tourists will be broadcast on BBC2 on Tuesday March 6 at 2100 GMT.